The Reasons of the Primary Judge
23 The primary judge's reasoning on this particular issue may be summarised as follows. According to Mr de Vos, the word "contact" imports into the claims the critical concept of the efficient transfer of forces, in that a robust tooth construction must be capable of efficiently and effectively transmitting forces from the covers to the support body: [256]. As a result of the large forces that are imparted on the teeth, it is necessary for those forces to be efficiently transmitted to the support body and the shaft in order for the teeth to be sufficiently robust, otherwise the large forces that are imparted onto the teeth during operation can cause the means of securing the covers to fail, and failure of tooth covers in between scheduled maintenance breaks is very undesirable: [257]. According to Mr de Vos, the most efficient way of transmitting force is a "compressive force", which involves pushing into, or compressing, a component, and as compressive forces do not rely on a fastening medium (unlike tensile and shear forces), it is preferable for the forces imparted on the covers during use to be transmitted to the support body through compressive forces: [258]. (A tensile force relies on a fastening medium to transmit the force between components, and involves pulling away from, or stretching, a component; a shear force is a transverse, rather than an axial, force: [96]-[97].) Mr de Vos observed that the Specification emphasises the importance of the ability of the tooth construction to transmit forces from the covers to the support body to ensure that the welds securing the covers do not fail as a result of the forces imparted on them during use: [259]. The primary judge considered that the emphasis on the effective transmission of force was inconsistent with the welds being the means for the transmission of the majority of the force as shear force, as depicted in the diagram which became known at the trial as Diagram 3 (Exhibit A11), which we have reproduced below:
The primary judge said that in the configuration as depicted in Diagram 3, the majority of the forces are being transmitted through the welds, thereby placing the welds under stress which may cause them to crack and fail early: [259]. The primary judge referred to the evidence of Mr de Vos to the effect that weld will most commonly fail where large shear forces or tensile forces are repetitively imparted on the weld (third affidavit of Mr de Vos at [853]). We note that MMD criticises the primary judge for not also referring to the evidence of Mr de Vos in that affidavit at [857], relevantly to the effect that in practice it is possible to create a tooth construction with clearances between the covers and support body provided that the cover is made with thick steel that is able to withstand the relevant forces even if there is a gap between the cover and the support body, the weld is thick enough, and the way the forces are transmitted to the support body does not place the welds under too much stress. The primary judge said that the person skilled in the art would be aware that mineral sizers undergo regular maintenance, and the tooth construction must be robust enough to break the ore and remain intact for the duration of the maintenance period: [260]. The welds must secure the covers of the tooth construction for the entire maintenance period, but as the tooth constructions are replaced at regular intervals, there is no need for the tooth constructions to be made to last as long as possible: [260].
24 The primary judge said that all of the words in the phrase "seated in face to face contact" have a role to play: [261]. The primary judge considered MMD to be focusing on the face of the support body as the face of interest, and referred to its submissions speaking of methods to ensure the requisite transmission of force "from the covers" to the support body, not the faces of the covers or the faces of the support body (as the claims require): [262]. The primary judge referred to Diagram 3 as depicting an arrangement where the rear cover does not directly touch the rear face of the support body. The primary judge said that the words "face to face" contemplate the existence of two faces (the face of the front (or rear) cover, and the front (or rear) face of the support body), and said that being in face to face contact required the two faces to be in physical contact: [262]. The primary judge observed that each time the phrase "face to face contact" is used, it is in the context of a description of the placement of two faces: the front or rear cover, and the front or rear face of the horn. In contrast, the discussion of welding in the specification refers to welding "to the horn", not specifically to the front or rear faces of the horn: [263]. The primary judge observed that the phrase "face to face contact" first appears at page 5, line 11, in the description of the placement of the rear cover in the first embodiment, in which the rear cover is described as being seated in face to face contact with the rear face of the horn: [264]. The primary judge observed that there is no mention of how the rear cover is held in place until the next paragraph in which the rear cover is said to be preferably secured to "the horn" (not the rear face of the horn) by welding, and it is also noted that the rear cover may be "indirectly welded to the horn" by being welded to the side covers: [264]. The primary judge said that later on page 5, line 30, the internal face of the top cover is said to be seated in "face to face contact" with the front face of the horn, and the top cover is then said at page 6, line 18, to be "secured to the horn 12, preferably by welding": [265]. The primary judge observed that there is no reference to a particular face of the horn, and said that the welding direction is to join the opposed faces between the top cover and the plate-like body of the side cover to one another: [265].
25 The primary judge expressed the view that "seated" in the phrase "seated in face to face contact" means positioned: [266]. The primary judge then said that the front cover is the front cover which is in physical contact with the front face of the horn: [266].
26 The primary judge referred to the specification as describing a method or sequence of the construction of the tooth construction, in which the cover is described as being "seated in face to face contact" with the relevant face of the horn, well before any discussion of how it is secured to the horn: [267]. That point was developed further by the primary judge at [280], in which her Honour referred to the Specification as speaking of weld as a preferable way to secure the covers of the tooth construction, but saying nothing about the transmission of forces through welds or the adjustment of the welds to bear transmission of the majority of the force as shear forces. The primary judge said that if welds were contemplated by the inventor as components through which large forces were intended to be transmitted efficiently to the horn and thereby effect face to face contact, it would be expected that the patentee would have said something about that topic, including in relation to the importance, size and nature of the welds required to effect the invention: [280]. Further, on the same hypothesis, the primary judge also said that the specification's sequence of construction would not describe components as seated in face to face contact before welding had taken place. The primary judge observed that welding is said in the specification only to secure the components after they are seated in face to face contact, referring at [280] to page 5, lines 10-17; page 5, line 29 to page 6, line 3; and page 8, line 27 to page 9, line 4 (to which reference may be added to similar statements at page 6, lines 13 to 20; page 7, lines 13 to 19; and page 9, lines 23 to 27).
27 The primary judge then turned to the topic of sand casting: [268]. The primary judge had earlier referred to three common forms of casting, being sand, die and investment casting: [101]. The primary judge referred to sand casting as having the advantages of relatively low production costs, and the ability to cast large components: [102]. However, sand casting is not a high-precision production method, and components that are produced using sand casting have relatively large manufacturing tolerances and relatively rough surfaces: [103]. The primary judge described die casting and investment casting as providing greater precision but involving more expense than sand casting: [105]-[106]. However, while investment casting was said to be more expensive than sand casting, the proposition was qualified in circumstances where the sand cast part is machined to increase its precision, as machining increases costs: [106]. The primary judge described machining as involving cutting the part into the desired shape using a variety of different tools and said that it was possible to increase the precision of a cast component by machining it after it has been cast: [107]. The primary judge referred to machining as being a labour-intensive process, which therefore adds substantially to the cost of producing the part, and so is usually only used when a high degree of precision is required: [107]. At [268], the primary judge referred to sand casting being relatively imprecise, and described components that are produced using sand casting as having relatively rough surfaces. In practice, the primary judge said that there will still be some clearances between the face of the support body and the front and/or rear covers due to the imprecision involved with sand casting: [268]. The front and/or rear covers will undulate across their surface, meaning that part of the face of the covers will touch the support body and part will not: [268]. The primary judge had earlier referred to the evidence of Mr de Vos to the effect that the covers of tooth construction are most commonly sand cast, and as the covers are sacrificial parts and designed to be replaced periodically, there is an imperative to minimise manufacturing costs: [121]. Further, as the covers do not have a particularly intricate design, Mr de Vos expressed the opinion that they were suitable for sand casting: [121].
28 The primary judge then expressed disagreement with the proposition that the expression "seated in face to face contact" required that the two faces must be "flush" to the extent that "flush" requires intimate contact across all surfaces of the faces, and referred to Dr Huggett's evidence that he contemplated that the majority of the surfaces would be in contact, rather than a perfect 100%: [269]. The primary judge also referred to the evidence of Mr de Vos that the surfaces of the covers are unlikely to be smooth, even with the best manufacturing tolerances, as cast surfaces are likely to have undulations, and over a lifetime of use and refurbishment (including gouging off old welded-on covers) the surfaces of the horn are unlikely to be entirely smooth or identical to each other: [270].
29 The primary judge next expressed the conclusion that a commonsense construction of "face to face contact" in the context of front and rear covers which are likely to be sand cast, means physically touching across most of the faces of the cover and the support body (allowing for undulations inherent in the casting process): [271]. The primary judge said that the same total force will be transmitted between two components, irrespective of whether they are "flush in intimate contact across their surfaces without any gaps" or there are some gaps between them: [271].
30 The primary judge then referred to weld as being discussed in the specification merely as the way to secure components, not as the primary conduit of force from the covers to the support body, referring to the method of construction outlined for the first embodiment: [272]. The primary judge said that there is no discussion in the specification of adjusting the weld to bear the transmission of the majority of the force as shear force if there is no physical contact across the faces of the covers and the support body: [272].
31 The primary judge criticised MMD's construction of Claim 1 as almost becoming a claim by result; that is, anything which achieves the functionality of, or results in, a robust tooth construction falls within Claim 1, even where it is an embodiment with only point to point contact with the side cover such as is shown in Diagram 3: [273]. The primary judge referred to MMD's submission that a robust tooth construction can be created that is designed to transmit forces between the covers and the support body entirely through weld (as in Diagram 3), and said that such a construction ignores the references to face to face contact in the specification and gives the word "contact" no work to do: [273]. The primary judge said that the submission also ignores the notion of efficient transmission of compressive forces, which was said by Mr de Vos to be imported by the word "contact": [273]. The primary judge said that where there is a permanent gap between a cover and a support body, the cover or weld could break during use, referring to Mr de Vos's evidence that the weld securing the cover to the support body may crack over time if there is a permanent gap between the cover and the support body, and, in his experience, welds will most commonly fail where large shear forces or tensile forces are repetitively imparted on the weld: [276]. The primary judge referred to Mr de Vos' agreement that where the rear cover and the rear face of the support body are "flush" (in the sense of contact across the majority of their faces), then the transfer of forces would be much more effective than when there is a gap such as that depicted in Diagram 3: [277]. The primary judge referred to MMD's submission that Diagram 3 shows that forces are transmitted from the rear cover to the peripheral sides of the rear face of the support body, and that although forces may only be transmitted to the outer few millimetres of the rear face of the support body, they are still transmitted to the rear face of the support body, which was said by MMD to be sufficient for the claims of the Specification: [278]. The primary judge then said that on MMD's case, the size of the weld is important because (in the Diagram 3 scenario) if the weld is only a few millimetres and is required to take a high amount of shear force, this renders it prone to cracking or failure, with the consequence that the cover is likely to fall off during operation: [279]. In that context, the primary judge made the observations, to which we have referred above, as to the Specification speaking of weld as a preferable way to secure the covers of the tooth construction, but saying nothing about the transmission of forces through welds or the adjustment of the welds to bear transmission of the majority of the force as shear forces: [280].