Surface finish definition

In rubber testing, the surface finish of metals is of importance, for example on mould surfaces and compression set plates. There are a number of standards in the ISO Geometric Product Specification series but the most relevant is ISO 428729 which covers terms, definitions and surface texture parameters relating to the profile method of measuring surface finish. There are apparently over 1000 different parameters to characterize surface finish30 but only a few are generally encountered. The most commonly found is Ra (previously called CLA) which is the mean deviation of the surface profile above and below the center line, followed by Rz, a measure of the peak to valley height. For example, the arithmetic mean deviation (Ra) of the compression plates for compression set tests must be better than 0.2 m. 

The results indicate that some surfactants can definitely lead to better surface finish upon polish. Table 5 gives the average RMS (root mean square) values, Ra, of surface roughness obtained with the Dektak profilometer. The measurements are carried out on both the copper disks and 4 inch copper wafers. Dramatic improvements are noticed in polished surface uniformity when surfactants Brij 35 and SDS are employed in the slurry. The destabilizing... 

The specification of a surface finish for stainless steel equipment is a source of many potential problems and misunderstandings between purchasers and manufacturers. The implications for costs and like-for-hke comparisons between tenders, and the need to establish that the equipment condition satisfies all functional requirements of the application, dictate that the surface finish specified should be appropriately defined in all contractual documents. Descriptions such as crevice-free or pohshed 400 grit , may appear definitive, but all too often lead to ambiguities, disagreements of interpretation, or unfitness for purpose. 

The definition of numerical parameters has been the most popular approach used to characterize surface finishing. They are traditionally based on two-dimensional data. This analysis is done by means of a profile which is obtained by a cross section of the surface. This profile comprises a set of points Xi, Zi], where x corresponds to the measured length along the direction of the profile and z is the height with respect to the reference line at each point. The selection of the profile s orientation, the number of points which defines it, the distance between them and the definition of the most adequate reference line to be used to measure the height are factors of great importance which go further than the scope of the current work. A detailed explanation can be found in [1]. 

VisibUity also includes clear definition of tread nosing and avoidance of surface finishes and textures that make one step blend in with another. 

The point of departure for this step, and therefore the end result of the fust step, is a definition of the plant in terms of what it should do and how well it should do it, the conditions under which it must be able to do it (what is shown as System Specification in Fig. B4.3), and any direct, physical requirements on the object, such as type of materials to be used (or avoided), surface finishes, weight and size restrictions, etc. The process of getting from the start to the finish of this second step has been developed and refined over the last couple of centuries, and we shall look at it in more detail in the next chapter. Here we just note that its main characteristic is a synthesis in terms of known construction elements, and for this reason it is often called the bottom-up process, this also serves to distinguish it from the process in the first step, the top-down design process, with which we shall mainly be concerned in this chapter. 

The selected process will produce a raw molded part that may or may not require surface preparation prior to coating. The surface finish may be limited by the inherent capabilities of the process. In general, higher pressure processes can produce better surface definition than processes that operate at low pressures. Push and squeeze type processes can often produce excellent surface definition and are capable of generating Class A surfaces or detailed grains out of the mold. 

The finish of flange facings varies with the manufacturer. For raised-face or male mating surfaces the finish usually consists of a continuous spiral groove formed by a round-nosed tool or a V tool (serrated finish). Female surfaces are smooth-finished (i.e., without definite tool markings). Other finishes are concentric-grooved, lapped, or mirror (cold-water). The latter two are usually for application without gaskets. 

An important advantage of the plastic is that in thermal processing the finish on the surface of the tool—whether it be matt, leather grain, jazzy pattern, or what you will—can be transferred directly to the workpieces. One proviso when a design is applied in this way is that the tool should not wear quickly (which will result in loss of definition of the decoration) or, worse, that it be scratched or damaged so that the unwanted mark is carried over to the products. 

This definition again invites further comment and elaboration. The implication may be that finishing is begun after a product is shaped by flow , but this is not always the case and the surfaces of many products are finished in part while compositions are hot or warm still. It mentions as examples six techniques for finishing but the Standard itself includes many more than this and it is worth remembering too that intermediates such as film, sheet, and mouldings (which require further fabrication before they become plastic products ) also must be finished satisfactorily the properties of the surface of an intermediate can be essential in obtaining the results required in the ultimate product. 

Liimited quality of surface definition and. product must be finished (deburred, etc.) after blowing. 

It is common to distinguish between internal and external lubricants. The worst definition is based on who adds the lubricant if the supplier added it, it comes to the processor as an internal lubricant if the processor must add it himself, it is an external lubricant. A semimeaningful distinction an internal lubricant is compounded into the polymer an external lubricant is applied to the surface of the mold. The proper distinction is based on miscibility/immiscibility of the additive in the polymer an internal lubricant is miscible with the polymer and acts like a small amount of plasticizer to increase molecular flexibility and mobility, and to help the disentanglement and flow of tbe polymer molecules in the melt. An external lubricant is immiscible in the polymer and tends to exude to the surface of the plastic and form an abhesive (nonstick) interface between the polymer and the steel process equipment, or it tends to come to the surface of the finished plastic product and give it continual lubricity in the use of the product. 

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