Crusher Base Frames: What the Weldment Has to Survive and How It Is Built
A jaw or cone crusher is a machine that hits its foundation several times a second for years. The base frame under it is not a static support. It is a fatigue-loaded weldment that also has to hold a machined plane flat while the machine tries to walk it out of position.
Most of the trouble buyers see with crusher bases traces back to treating them as ordinary structural steel. This guide walks through what the frame actually has to do, how shops build them and what belongs on the drawing before it goes out for quotes. If your part is in this category, the mining equipment frames page lists the spec call-outs we see most often.
What the base has to do
Three jobs, in order of how often they are underestimated:
- Carry the dynamic load without cracking. The crusher manufacturer publishes a dynamic load factor for the machine. It is often several times the static weight and it is applied at the operating frequency, every cycle, for the life of the plant. Every weld in the load path sees that cycle.
- Hold the mounting plane flat. The machine feet sit on machined pads. If those pads are not coplanar, the crusher frame is pulled into a twist when the bolts are torqued, and the manufacturer’s bearing life calculation no longer applies.
- Transfer the load into the foundation. Anchor bolts, grout pockets and the stiffness of the base itself decide whether the load reaches the concrete or bounces around in the steel.
A base that does the first two and not the third will loosen its own anchor bolts. A base that does the third and not the first will crack at the stiffener toes.
Plate, sections and the shape of the frame
Crusher bases are almost always plate weldments rather than rolled sections. Plate lets the designer put the material where the load is and gives a flat surface to machine afterwards.
Typical practice in published designs:
| Element | Common choice | Why |
|---|---|---|
| Top plate under the crusher feet | 40 to 80 mm, S355 or A572 Gr 50 | Machining allowance plus stiffness across the bolt pattern |
| Side and web plates | 20 to 40 mm | Shear and torsion resistance |
| Internal stiffeners | 16 to 25 mm, terminated short of the flange | Fatigue detail category |
| Anchor bolt sleeves | Pipe, welded to top and bottom plates | Allow bolt position adjustment at site |
The numbers above are typical of published crusher installation guides, not a design. Sizing is the machine manufacturer’s or the plant engineer’s job, and the shop that quotes builds to the drawing it receives.
The shape matters as much as the thickness. A closed box section resists torsion far better than an open channel of the same weight. Most crusher bases are built as a series of closed cells with access holes for welding and for later inspection.
Fatigue is the design driver
Structural codes handle fatigue through detail categories. EN 1993-1-9 and AS 4100 both classify weld details by how well they survive cyclic stress. The same two plates joined by a full penetration butt weld sit in a much better category than the same plates joined by a fillet weld with a stiffener ending on the flange.
For crusher bases, the details that decide the life are:
- Stiffener terminations. A stiffener welded right up to the edge of a flange creates a stress concentration at the weld toe. Terminating the stiffener short, with a soft radius, moves it to a better category.
- Weld toe profile. Toe grinding or TIG dressing on the fatigue-critical fillets improves category by removing the notch. It is cheap when done in the shop and impossible once the base is grouted.
- Attachments. Every bracket, lifting lug and cable tray support welded onto the base is a new fatigue detail. Anything that can bolt on should bolt on.
The drawing should state the loading condition as cyclic and name the detail categories it relies on. That tells the shop which welds get toe treatment and which welds get MT after welding. AWS D1.1 and AS/NZS 1554 both have cyclic loading clauses that change the acceptance criteria; the fabricator cannot apply them if the drawing does not invoke them. Our guide to weld standards in plain language covers what those clauses ask for.
Stress relief and why the sequence matters
A crusher base is welded, then machined. Between those two steps most designs call for thermal stress relief. Welding leaves residual stress in the plate; machining removes material and lets that stress redistribute; the base moves. Stress relieving before machining means the base moves in the furnace, where it does not matter, instead of on the mill.
The sequence that works:
- Fit and weld the full weldment.
- Post-weld heat treatment, typically 580 to 620 °C for carbon steel with a hold time per plate thickness, in a furnace large enough to take the whole base.
- Rough machine the pads.
- Finish machine the pads in one setup.
The furnace is the constraint. A base that is 4 m by 3 m needs a furnace that size. Shops that do not have one either subcontract the relief or propose vibratory stress relief. Vibratory methods have their place, but for a fatigue-loaded base that also needs dimensional stability, most specifications insist on thermal. The stress relief guide goes deeper on when each method is acceptable.
Machined pads and coplanarity
The crusher’s feet have to sit on a common plane. The usual call-out is a flatness or coplanarity tolerance across all pads, in the order of 0.05 to 0.1 mm per metre, with a note on the shim allowance permitted at installation.
Two things go wrong here:
- The pads are machined in separate setups. Each setup is flat to itself but not to the others. Insist on a single setup, or on a laser tracker check after machining if the machine table cannot hold the whole base.
- The base is machined before it is fully welded. Sometimes a late bracket is added after machining. That weld pulls the pad out of plane. All welding finishes before machining starts, with no exceptions.
Ask for the machining inspection report as part of the delivery. A laser tracker or large CMM report showing every pad relative to the datum plane is the only real evidence that the base is what the drawing asked for. Our dimensional inspection guide explains what the report should contain.
Anchor bolts and grout
The base reaches the concrete through anchor bolts and grout. Details that save site time:
- Bolt sleeves that allow the bolt to be moved a few millimetres after the base is set, so that the foundation drawing and the base drawing do not need to agree to the millimetre.
- Grout pockets or grout holes in the top plate so that the grout can be poured and checked for voids.
- Levelling screws or shim packs designed in, not improvised on site.
A base that has been designed for grouting saves days at installation. A base that has not been will still get installed, but nobody will be happy about how.
Transport: the base is usually oversize
A base for a mid-size cone crusher is typically wider than a flat rack container. That leaves three options: breakbulk shipping, a split-and-bolt design or an oversize road move at both ends. Each has a cost, and the cost is best known before the design is frozen.
Split-and-bolt is the usual answer for export. The base is built as two or three pieces with machined mating faces and a bolted joint designed for the dynamic load. The pieces fit in a container or on a flat rack, and the joint is made up on site. The split-and-bolt guide covers how the joint is designed and what it does to the machining sequence.
What to put on the drawing
Before a crusher base goes out for quotes, check that the drawing states:
- Material grade with the certificate level required (EN 10204 3.1 is usual).
- The weld standard, with the loading condition marked as cyclic.
- Detail categories or, at minimum, which welds need toe treatment.
- NDT extent: MT on fatigue-critical fillet toes, UT on butt welds in tension, with acceptance criteria.
- Stress relief method and the point in the sequence where it happens.
- Pad flatness and coplanarity, with the datum and the inspection method.
- Anchor bolt sleeve details and grout provisions.
- Surface preparation and coating system, usually ISO 12944 C4 or C5 for a mine site.
- Transport split, if any, and the maximum piece dimensions.
A drawing that carries all of that gets comparable quotes back. A drawing that does not gets quotes that each assume something different, and the cheapest one usually assumed the least.
Sending it out
If you have a crusher base drawing ready, send it through the RFQ form with the destination port. We check which shops in the network clear the crane, furnace and machine table it needs, and within 24 business hours up to three of them quote you directly. The mining equipment frames page lists what else the network places for this sector.